In general, an air conditioner for a vehicle includes a cooling system for cooling the inside of the vehicle and a heating system for heating the inside of the vehicle.
The cooling system includes converts air blown from an air blower into cold air through heat exchange between refrigerant, which circulates a condenser, a receiver dryer, an expansion valve and an evaporator in order and returns to a compressor by operation of the compressor, and the blown air passing the surface of the evaporator by the air blower and discharges the cold air to the inside of the vehicle in order to cool the inside of the vehicle.
Moreover, the heating system introduces cooling water to a heater core and exchanges heat with the air blower in order to heat the inside of the vehicle.
Such an air conditioner for the vehicle is classified into three types.
One of the three types of the air conditioner is a three piece type air conditioner where a blower unit, an evaporator unit and a heater unit are disposed independently. However, such a three piece type air conditioner has various disadvantages in that it is deteriorated in utilization of the inside space of the vehicle because it is large-sized and in that it is deteriorated in productivity.
Therefore, in order to increase effectiveness of the inside space of the vehicle, a small-sized air conditioner for a vehicle is being demanded, and in response to such a demand, recently, a semi-center mounting type air conditioner where the blower unit and the heater unit are mounted integrally or a center mounting type air conditioner where the blower unit, the evaporator unit and the heater unit are mounted integrally is increasing in use.
FIG. 1 illustrates an example of a conventional semi-center type air conditioner, and in FIG. 1, the blower unit is not illustrated.
The air conditioner 1 for the vehicle shown in FIG. 1 includes: an air-conditioning case 10 having a defrost vent 11, a face vent 12 and a floor vent 13 which are formed at an outlet side and are air discharge ports of which the degree of openings are regulated by a mode door 14; a blower not shown) connected to an inlet side of the air-conditioning case 10 for sending inside air or outside air; an evaporator 2 and a heater core 3 that are mounted inside the air-conditioning case 10; and a temperature-adjusting door 20 for adjusting the degree of opening of a cold air passageway P1 which bypasses the heater core 3 and the degree of opening of a warm air passageway P2 which passes through the heater core 3.
The temperature-adjusting door 20 includes: a sliding door 21 which is mounted in sliding grooves 16 formed at both sides of the inside of the air-conditioning case 10 to be able to slide and has a gear part 21a formed on one side thereof; and a gear shaft 22 which is rotatably connected to a through holes (not shown) formed at both sides of the air-conditioning case 10 and has a gear part 22a gear-coupled with the gear part 21a of the sliding door 21 so as to operate the sliding door 21.
Furthermore, the mode door 14 has a structure similar with the structure of the temperature-adjusting door 20. In brief, the mode door 14 includes: a sliding door 14a connected to both sides of the inside of the air-conditioning case 10 to be able to slide; and a gear shaft 14b rotatably mounted at both sides of the inside of the air-conditioning case 10 and interlocking with the sliding door 14a so as to operate the sliding door 14a. 
The temperature-adjusting door 20 and the mode door 14 are rotated by being connected to an actuator (not shown) mounted on the outer face of the air-conditioning case 10 so as to adjust the degree of opening of the cold air passageway P1 and the degree of opening of the warm air passageway P2 or to open and close the vents 11 to 13 and 15.
According to the air conditioner 1 having the above structure, in a case of the maximum cooling mode, the temperature-adjusting door 20 opens the cold air passageway P1 but closes the warm air passageway P2. Additionally, in a case of the maximum heating mode, the temperature-adjusting door 20 closes the cold air passageway P1 but opens the warm air passageway P2.
Therefore, in the maximum cooling mode, it blown by the blower (not shown) is converted into cold air by exchanging heat with refrigerant flowing inside the evaporator 2 while passing the surface of the evaporator 2, and then, flows toward a mixing chamber (MC) through the cold air passageway P1. After that, the cold air is discharged to the inside of the vehicle through the vent opened by the mode door 14 according to air discharge modes including a vent mode, a floor mode, a defrost mode, a bilevel mode and a mixing mode in order to cool the inside of the vehicle.
Moreover, in the maximum heating mode, the blown air is converted into warm air by exchanging heat with cooling water flowing inside the heater core 3 while passing through the heater core 3 through the warm air passageway P2, and then, flows toward the mixing chamber (MC). After that, the warm air is discharged, to the inside of the vehicle through the vent opened by the mode door 14 according to the air discharge mode in order to heat the inside of the vehicle.
In the meantime, in a case of the mixing mode, the temperature-adjusting door 20 is rotated to a neutral position, and opens all of the cold air passageway P1 and the warm air passageway P2. Therefore, cold air passing through the evaporator 2 and warm air passing through the heater core 3 flow toward the mixing chamber (MC) and are mixed together, and then, the mixed air is discharged to the inside of the vehicle through the vent opened by the mode door 14 according to the air discharge mode.
Furthermore, the air conditioner 1 prevents air leak between the inner face of the air-conditioning case 10 and the sliding door 14a because the sliding door 14a of the mode door 14 is compressed to the inner face of the air-conditioning case 10 by wind pressure of the inside of the air-conditioning case 10 so as to be face-sealed.
However, the conventional air conditioner 1 has a problem in that some of air leaks from the face-sealed part due to deformation of the inner face of the air-conditioning case 10 or the sliding door 14a even though the sliding door 14a is face-sealed with the inner face of the air-conditioning case 10.
Furthermore, because of the nature of the face sealing, because an interval between the sliding door 14a and the inner face of the air-conditioning case 10 is very small or the sliding door 14a gets in contact with the inner face of the air-conditioning case 10, the sliding door 14a is vibrated by air induction and wind pressure, and especially, an end portion of the sliding door 14a is intensified in vibration when it gets farther from the gear shaft 14b. 